When natural gas is processed, it provides a liquid stream where your propane, ethane, and numerous other "thanes" are included. It was originally sold as natural gasoline, so people started calling it gas since it came from natural gas. It had an octane of about 40 or 50--would not work in today's cars. It was not too long before the natural gas industry learned that by compressing the gas, it would get cold and as soon as the compression was removed, the liquids would drop out (the actual process is more complicated.) The result was we had natural gas and gas, which is short for gasoline as someone noted. Europeans refer to petrol, but that is often diesel fuel that like gasoline, comes from petroleum.
Gas became the common name for gasoline. Thus we had gas cans, gas stations, gas-powered lawn mowers and so-on. Technically, we should it gasoline. I know when I worked for the petroleum industry, I often had to get reporters to clarify if their question was about natural gas or gasoline.